The proposed research is intended to gain understanding of the reasons underlying obligate interdependence between insects and microorganisms. Experiments are proposed for studying the interactions of Blattella germanica and its intracellular symbiotes as a model of parasitism dependent on arthropod vectors. Two categories of systems will be used: cell culture in vitro, and analyses during certain defined phases of development of the host insect. Tissue and cell culture systems will be used for analyzing the dynamics of infection by the symbiote and the host cell reactions, which may be either cooperative or defensive. The resulting data will provide information as to the characteristics of cells in arthropod vectors that make them susceptible or non-susceptible to intracellular parasites. Attempts will be made to correlate the development of the host's immune reactions, with enzymatic and bactericidal assays, on the cyclic phases of growth of the symbiote. Symbiotic involvement in reproduction will be studied on the organismic level. Contributions of the microorganisms in the production or sequestration of vitellogenin will be sought with biochemical extractions and organ cultures. The infectious and growth phases of symbiote development will be examined with electron microscopy of gonadal germ tissue and embryos. Purified B-lactoglobulin, or the peptide fractions that result from its hydrolysis, will be tested for its growth promoting effect with aposymbiotic insects.